Control of the localized electrochemical dissolution of solid-state sintered silicon carbide – SiCECM

• Applicants: Professor Dr. Alexander Michaelis; Professor Dr.-Ing. Andreas Schubert
• Subject Area: Metal-Cutting and Abrasive Manufacturing Engineering ; Glass, Ceramics and Derived Composites
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 527413836

Due to their very good mechanical, tribological and corrosion-resistant properties, solid-state sintered SiC ceramics (SSiC) are used, for example, as mechanical seals or valves in power plant construction and chemical industry. However, their high hardness and compressive strength make mechanical shaping and surface treatment difficult. The high melting point impairs thermal machining by spark erosion or laser ablation. Electrochemical machining (ECM) represents a promising alternative due to the subordinated influence of mechanical and thermal workpiece properties. But there are currently severe limitations with regard to applicable machining parameters for targeted shaping and surface structuring. Own preliminary studies of both applicants prove basic solutions for anodic dissolution of SSiC with sufficiently high electrical conductivity for the required charge exchange. Passivating layers are formed, and dielectric breakthrough occurs with considerable formation of oxygen through electrolysis at sufficiently high electric potential. More detailed investigations into oxide layer formation and dissolution, possible side reactions and pH value changes as well as effects on the instability of the passive layer are not yet known, and there is no uniform description of the ECM in thermodynamic imbalance. In addition, the observed influence of Joule heating on the removal rate due to the semiconductor properties of SSiC has not yet been investigated. Jet-ECM enables the application of sufficiently high voltages and individual electrolyte composition for the dissolution of SSiC with high localization through strongly focusing the current flow and thus represents a promising method for researches on surface structuring. However, predictable ablation geometries and the impact of local Joule heating on the current efficiency are not known. In order to analyze relevant, interacting field quantities and field quantity distributions in sufficiently small time scales and geometry dimensions and to understand their relationships, numerical simulation models appear useful and necessary. The main goal is the fundamental research of the influences of process input parameters on the anodic dissolution of SSiC for simulation-assisted design of micro-structuring by Jet-ECM. For this purpose, the trans-passive breakthrough and removal continuity at lower electric potential will be investigated. Basic knowledge gained in a micro-capillary cell shall provide the necessary input parameters for the development of a simulation model for the scaling of Jet-ECM processing parameters. The oxygen evolution and carbon reaction shall be quantified in order to derive the oxidation states of Si and C and their stoichiometry and to control the removal geometry.

• DFG Programme: Research Grants